Sickle cell anemia is an autosomal recessive disorder and the most common genetic disease affecting African-Americans. Approximately 0.15% of African-Americans are homozygous for sickle cell disease, and 8% have sickle cell trait. Acute pain crisis, acute chest syndrome (ACS), and secondary pulmonary hypertension are common complications of sickle cell anemia. Mortality rates of sickle cell patients with pulmonary hypertension are significantly increased as compared to patients without pulmonary hypertension. Recent studies report up to 40% mortality at 22 months after detection of elevated pulmonary artery pressures in sickle cell patients. Furthermore, pulmonary hypertension is thought to occur in up to 30% of clinic patients with sickle cell anemia. This study is designed to determine the prevalence and prognosis of secondary pulmonary hypertension in adult patients with sickle cell anemia and to determine whether genetic polymorphisms in candidate genes contribute to its development.